Research On Resistive Characteristics Of Graphene/NiO-based RRAM

With the development of science and technology,people demand more and more memory performance,and the traditional memory can no longer meet people's needs.Therefore,a variety of new memory came into being.Among them,RRAM,which has the advantages of simple structure,fast read and write,low power consumption and compatibility with the traditional CMOS process,has drawn much attention.However,due to thick resistive layers and electrodes,the volume reduction of RRAM is not obvious at present,and there is not enough research on the ultra-low power consumption and ultra-high integration of RRAM.Graphene has become a research hotspot due to its excellent performance,and graphene has been used more and more in RRAM.Among them,the RRAM of graphene/NiO/graphene structure is found to have the advantage of drastically reducing the device size and drastically reducing the power consumption.However,it is unclear whether the interface between the different graphene crystal and NiO will affect the performance of the RRAM device,and which one has the best combination of graphene and NiO,Therefore,in this paper,the first-principles principle is used to explore the effect of different crystal facets on the resistivity of NiO and the influence of different graphene on resistivity-change characteristics,so as to find the ideal graphene crystal phase.For this reason,six different interfaces namely,armchair Graphene(aGNR),zigzag Graphene(zGNR),and surface defect zigzag Graphene(zGNR1)nanoribbons with uni-and bilaminar<001>-oriented NiO were studied.First,the Mulliken mean and difference populations,the interface energy,and the interface adhesion energy of six interface structures were calculated by the Cambridge sequential total energy package(CASTEP).The aGNR/NiO interface showed higher interface adhesion energy and Mulliken population mean as compared to the other interface structures(i.e.,aGNR/NiO was more compact than the rest of interfaces).Moreover,the lowest interface energy and Mulliken difference population values along with the negligible aberration state clearly revealed aGNR/NiO to be the best interface among those studied herein.Through the optimized results of each interface structure and electron density,charge density difference and LDOS(local density of states)analysis comparison found that excessive distortion of graphene/NiO interface will lead to the formation of the interface becomes more difficult,and will lead to the generation of dangling bonds at the interface,which leads to the decrease of the Mulliken population average values of C-O bond C-Ni bonds at the interface,the combination of the two materials is not close enough,and the stability of the interface structure system becomes worse.The strong covalent bond at the aGNR/NiO interface is an important guarantee for the stable interface.Moreover,the Mulliken population of C-O bonds at the interface is very high and has a stronger covalent bond property,which greatly promotes the stability of the interface.Subsequently,the current-voltage(I-V)curves indicate the aGNR/NiO/aGNR device presents memory effect while tracing the path back in the current data,but not switching between positive and negative voltages due to the device unipolar behavior and the aGNR/NiO/aGNR structure is found to present lower current in low resistance state and has some advantages in low power than other devices based on Graphene and NiO.The mechanism of resistive switching is demonstrated by performing density functional tight binding and much more(DFTB+)dynamics.It is found that the high and low resistance changes of graphene/NiO/graphene RRAM are caused by the conductive and fuse of conductive filaments formed by Ni in the resistive layer of NiO.And found that the number of Ni atoms of the aGNR/NiO/aGNR structure for forming the conductive filaments in the low-resistance state is smaller than that of the other types of graphene/NiO/graphene structure,resulting in low power consumption of the structure.The special structure of the armchair graphene and close C-O bonds at the interface effectively reduce the number of Ni atoms used to form the conductive filaments.Finally,the performance characteristics of aGNR/NiO/aGNR devices were further studied by widening and doping oxygen atoms in aGNR/NiO/aGNR RRAM devices.By widening the aGNR/NiO/aGNR,it is found that as the width of the device increases,the high-resistance state resistance gradually decreases and the low-resistance state value gradually decreases.But as the device width increases to a certain degree(about 1:1),the low resistance value will remain stable.As the width of the device increases,the ratio of the high and low resistance states decreases,indicating that the gap between the high and low configuration resistors is shrinking and the device becomes more misread.Therefore,the device width should not be too large,should maintain a reasonable aspect ratio.By doping at the interface between graphene and NiO,it is found that the stability of the device tends to decrease dramatically due to the incorporation of Ni,and the stable graphene/NiO interface can not be formed.Therefore,the study on the electrical properties of the device only considers the interface O-doped at the situation.It is found that the incorporation of O at the interface is conducive to the reduction of device power consumption,but the ratio of high resistance state to low resistance state will continue to decrease.O excessive incorporation risks being misread during operation.In summary,the results of this paper provide a method and enlightenment for improving the performance of graphene/NiO/graphene RRAM,and have theoretical guidance for experimental research.